Slide valves or sleeve valves are widely known in the art and are used in many different applications to control the fluid flow within a particular environment. Although a variety of sleeve valve designs exist, each comprises a common component or element that exists in one form or another, namely a type of sliding or rotating or otherwise movable sleeve that opens and closes, or otherwise regulates, a fluid passageway.
Sleeve valves are particularly known to operate within extreme environments, such as high temperature and high pressure environments, although many sleeve valves or sleeve valve designs have been found to be beneficial in less extreme environments as well. In any event, as a fluid is forced to flow within a conduit-type structure (e.g., a pipe, hose, etc.) it is accompanied by a corresponding or associated fluid pressure. This fluid pressure must be properly contained and sufficiently regulated in order to maintain the integrity of the system in which it is present and in which the fluid is flowing. Therefore, any valves present within the system must also be capable of receiving and supporting the fluid and its associated fluid pressure. As a product of their efficient design and relatively simple operating mechanisms, sleeve valves are widely used to control the flow of fluid within pressurized environments. As a drawback to being used in such pressurized environments, however, the fluid pressures existing within the sleeve valve are capable of exerting significant forces on the movable sleeve, particularly if the movable sleeve is supported by one or more seats. If seated, the movable sleeve experiences additional forces acting upon it from the structural elements of the seats. These forces are created by the high pressures existing within the valve that cause the movable sleeve and the supporting seats to compress against one another. Thus, sleeve valves often comprise a movable sleeve that is not easily actuated and that is adversely affected by the fluid pressures existing within the sleeve valve. To overcome these pressures, many sleeve valves are operably connected to some type of powering means used to actuate the movable sleeve. For instance, high power mechanical, electromechanical, and other similar power-assist devices and systems are often employed, wherein the presence of these devices or systems is more than one of convenience merely to eliminate the need to manually operate the valve. Indeed, a primary purpose of these power assist devices and systems is to overcome the often significant fluid pressures and resultant inertial structural forces acting upon the movable sleeve. Overcoming these inertial forces enables the movable sleeve to be actuated and the sleeve valve opened and closed as needed.
Other sleeve valves may or may not be manually actuated. Similarly, because of the fluid forces accompanying any type of forced fluid flow, manually operated sleeve valves are limited in their applications in that only low pressure fluid flows may be accepted or received therein. A high pressure fluid flow would either bind the movable sleeve so that it cannot move, or significantly hinder its ability to move as a result of the forces acting upon the movable sleeve contributing to its resistance to any displacement or actuation.
Fluid control is important in closed-loop and other similar applications. In these applications, it is common to employ a servovalve to provide the means for controlling the fluid. A servovalve is a device used to provide fluid control typically in a continuously acting, bi-directional closed-loop system. A servovalve provides servocontrol, which is control actuated by a feedback system. In short, an output signal is compared to an input or reference signal, wherein corrections are made by the servovalve to correct any differences between the two. The feedback signal may be provided by fluid pressure, mechanical linkage, electrical signal, or a combination of these.
One particular application in which servovalves are common is in hydraulic systems. Many control systems employ hydraulic elements for control of a larger object system. The power supply in such object systems is normally in the form of a pump, but the application of power is controlled by a servovalve. The servovalve controls the rate, including direction, of hydraulic fluid flow and effectively functions as the interface between the hydraulic elements and the control elements.